SummaryThe plasminogen levels and the reactivities of plasmas in two commonly used blood coagulation tests have been compared for man and seven mammals. The plasmas of three nonhuman primates in general reacted as did human plasma in tests for plasminogen activation and in reactivity in the partial thromboplastin time test. The dog had the highest level of plasminogen, and the goat the lowest, of the eight species tested. Overall, the pig appeared to have the most reactive blood coagulation mechanism, clotting the fastest and lysing the slowest, while man's was among the least reactive in clotting and intermediate in lytic activity of those tested. Aside from the nonhuman primates, the calf's clotting and lytic mechanisms resembled those of man more nearly than did those of the other mammals tested. The influence of these species differences on selection of animals for in uzio evaluation of blood vascular prosthetic materials and devices is discussed.

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Heparin neutralizes the inhibitory effect of prostacyclin (PGI2) on platelet aggregation. The PGI2-induced enhancement of platelet cyclic adenosine monophosphate levels is also inhibited. The mechanism appears to involve a direct interaction in which heparin neutralizes the inhibitory effects of PGI2 on platelet aggregation but, at the same time, does not lose its own anticoagulant activity. These findings may explain instances in which heparin infusions have been reported to produce hyperaggregation of platelets, thrombotic episodes, and thrombocytopenia in patients.